1. Field of the Invention
The present invention relates to an image processing apparatus for correcting an image.
2. Description of the Related Art
As is commonly known, some conventional image processing apparatuses employ a method of correcting the tone of a display image by luminance value conversion using histogram equalization. In such an apparatus, the correction amount becomes greater as the frequency of the histogram of the luminance value in an input image increases. In a region having high-frequency components, i.e., a region including a complex pattern(texture), a given correction amount is applicable to enhance the pattern and perform desirable correction. However, in a region including a monotonous pattern, applying the same correction amount makes a tonal jump recognizable.
To prevent this, methods have conventionally been proposed which equalized a histogram by limiting the correction amount in a tonal range where frequencies concentrate. For example, a method disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2006-217424 detects one or more luminance ranges where frequencies concentrate and limits the dynamic range after correction in each range, thereby preventing overcorrection in a shifted histogram of luminance signals Y.
However, the above-described conventional image processing apparatus cannot determine whether a region should be enhanced or not because region determination is based only on the distribution of a histogram. Consequently, it can only perform adjustment to reduce the correction amount.